1. Hollaender, A., Stapleton, G. E., and Martin, G. L., Nature, 167, 103 (1951).
2. Howard-Flanders, Paul, Advances in Biological and Medical Physics, 6, 553 (Academic Press, New York, 1958).
3. Dale, W. M., Davies, J. V., and Russel, C., Intern. J. Rad. Biol., 4, 1 (1961).
4. Hoffmann, A. K., and Henderson, A. T., J. Amer. Chem. Soc., 83, 4671 (1961).